The present invention relates to an injector driving control apparatus for use in controlling a fuel injector for supplying fuel to an internal combustion engine; and, more particularly, the invention relates to a technique for achieving a wide dynamic fuel pressure range by controlling the fuel injection volume according to the waveform of the current being generated to drive the injector, instead of changing, in a wide range, the fuel pressure of the fuel supplied to the injector.
As set forth in Japanese Application Patent Laid-Open Publication No. Hei 06-241137, two target current levels for the initial phase of magnetic attractor, namely, a high current target value and a low current target value, are determined by excitation current control corresponding to changes in fuel supply pressure, and, thus, the durability and reliability, as well as the efficiency of operation of fuel injection solenoid valves are improved.
The injector controls the injection volume according to the time during which the current is to be supplied. In an operation that ensures linearity (proportionality between the current supply duration and the fuel injection volume of the injector) in a wide fuel pressure range, the following events occur.
The time from the start of supply of the current to the actual opening of the valve, that is, the delay in the opening timing of the valve, differs between a low fuel pressure state and a high fuel pressure state.
After valve opening, the time from the end of supply of the current to the actual closing of the valve has a relationship with the coil current value which exists during the end of supply of the current. In this regard, and as the coil current value at this time increases, the time to the actual closing of the valve (namely, the delay in the closing timing of the valve) becomes longer, with the result that the amount of fuel injected during this time increases.
These events, in turn, create the following problems.
If the current value is set for a low fuel pressure, increases in the fuel pressure will prevent the valve from opening, or, even if the valve opens, there will be a great delay in the opening of the valve. Therefore, with such a delay, since the application of a voltage higher than the battery voltage will have been completed by the time the valve opens, it will not be possible for the open status of the valve to be maintained. This problem relates to the duration of the current waveform.
Conversely, if the current value is set for a high fuel pressure, decreases in the fuel pressure will cause the valve to close too early. If the current supply duration is reduced in order to inject a smaller amount of fuel, the supply of current will be terminated when the current value is high, in spite of the fact that the application of a voltage higher than the battery voltage will not yet have been completed. In such a situation, compared with the situation in which the current supply duration increases and the supply of current is terminated with a low current value, the valve closing delay time increases, and this, in turn, increases the injection volume and deteriorates the linearity in a small injection volume region. This problem relates to the current value of the current waveform.
Also, the coil of the injector needs to have a low resistance and a low inductance to improve the valve opening/closing response of the injector.
Even if the application of the technique disclosed in conjunction with FIG. 4 of Japanese Application Patent Laid-Open Publication No. Hei 06-241137 is to be attempted for solving the above-described problems, since these techniques involve the use of a coil that is low in inductance, unless the high target current value is changed significantly, it will not be possible to avoid the above-described problem relating to the duration of the current waveform. Therefore, in view of the scale of the circuit elements and the heat produced therefrom, the application of the above-described technique is not realistic. Also, even if the application of the techniques disclosed in conjunction with FIG. 9 of Japanese Application Patent Laid-Open Publication No. Hei 06-241137 is to be attempted, such techniques cannot be adopted, since increases in the duration application of a voltage higher than the battery voltage will reduce the boost voltage and generate a great amount of heat.
To solve the problems described above, it is necessary to adjust either the current value of the coil, when a boost voltage is not applied thereto, or the duration of a large current value. More specifically, the coil current needs to be increased to a great enough value by applying a boost voltage to open the valve; and, immediately after the valve has opened, a closed circuit is formed by the coil of the injector and a current feedback diode (current free-wheel diode). After this, the magnetic energy stored within the coil is utilized to maintain the energized status of the valve without a voltage being applied, and this feedback duration of the current is adjusted according to the fuel pressure obtained.
For this reason, the injector driving control apparatus according to the present invention comprises an injector for supplying fuel to an internal combustion engine, a switching means for energizing the coil of the injector with current from a battery, a control circuit for controlling the switching means, a means for detecting the current flowing through the coil of the injector, a current feedback diode (current free-wheel diode) for feeding back the coil current of the injector, and a means for abruptly reducing the coil current of the injector. These elements are designed to operate so that a voltage is supplied to the coil of said injector from the start of energization to the attainment of a first target current value; then control is provided so as to stop the application of the voltage temporarily upon attainment of said first target current value and so as to supply the appropriate current by forming a closed circuit composed of the coil and said current feedback diode (current free-wheel diode); and, thereafter, the abrupt current reducing means is activated so as to ensure that the current value, when greater than a second current value that is smaller than said first current value, is reduced, and then that the appropriate voltage is applied to obtain said second current value.
The operation timing of the abrupt current reducing means is determined by performing a comparison between a coil current value that has been detected by said detection means and a value that has been set. The operation timing can also be changed according to a timing command signal sent from said control circuit.
In addition, there is provided a means for detecting the pressure of the fuel supplied to the injector; and, when the fuel pressure increases, the operation timing of the abrupt current reducing means will be changed for delayed operation.
Also, the coil current follow-up control section for obtaining each of said target current values is constructed so that the first stage of the control accomplishes energization by applying a boost voltage that is higher than the voltage of said battery, and so that the second stage of the control accomplishes energization by applying the battery voltage.